The present invention relates to methods of employing an optical system for determining the angular position of a radiating point source as well as the system itself. The disclosure of the parent application identified above is hereby incorporated by reference herein. In the present invention, radiation from a point source travels through a mask and onto the surface of a sensor. In the prior art, this general concept is well known, however, the prior art fails to teach or suggest the specific techniques employed by Applicant to accurately measure angular position and distance using such a structure.
Prior art systems have used masked or coded apertures placed above multi-element detectors. All of these techniques have attempted to determine the position of a projected pattern on a detector surface by comparing signals from fixed detector elements arranged in a unique pattern or from comparison to fixed reference signals previously stored in a computer.
The present invention employs a transmissivity mask with a plurality of sinusoids of different scale to achieve high image detection resolution, and corresponding high angular resolution.
The following prior art is known to Applicant:
U.S. Pat. Nos. 4,193,689 and 4,314,761, both to Reymond et al. disclose arrangements for locating radiating point sources including the use of a single axis detector array and an aperture mask containing a slit to project light onto the array. In the earlier patent, a cylinder lens is used, and in the later patent, the cylinder lens is replaced with an aperture that can be shuttered to allow light in from preferred directions. In each case, three single axis arrays are used, and three cameras are required to compute three planes that intersect to define a point in space. The embodiments of the present invention differ from the teachings of the Reymond et al. patents since they include computing means to determine scales and shifts of image components and wherein the mask does not include a single slit.
U.S. Pat. No. 4,209,780 to Fenimore et al. and U.S. Pat. No. 4,389,633 to Fenimore disclose the technique of using uniformly redundant arrays for coded aperture imaging. Correlation between mask and image is used to determine a lag function of the received mask pattern. A mosaic pattern is disclosed as yielding results superior to those yielded through the use of a random array. In the Fenimore '633 patent, the mask and detector are either one or two dimensional. The Fenimore '780 patent only discloses two dimensional imaging. The present invention differs from the teachings of the Fenimore patents since it does not compare an image to a fixed reference pattern.
U.S. Pat. No. 4,435,838 to Gourlay discloses the concept of imaging planes of various distances in the field of tomographic imaging. The Gourlay technique improves the prior art process of selecting various image sizes to correlate with detector response to select a particular depth plane. Gourlay teaches the setting of a coded aperture at a distance D/d, where D is the object-to-detector distance and d is the object-to-mask distance, so that the image can be kept at the same magnification, thereby simplifying the correlation process. The present invention differs from the teachings of Gourlay and other prior art systems in the field of tomographic imaging, since, in the present invention, various object-to-mask distances or various image sizes are not chosen to select a particular depth, but, instead, the mask image scale is automatically determined using frequency domain techniques.
Applicant is also aware of U.S. Pat. No. 5,408,323 to Mitchelson and U.S. Pat. No. 6,141,104 to Schulz. Each of these references teaches the concept of the use of a random pattern mask or universal redundant array. In each of these patents, measurement is conducted by comparing actual measurements to previously stored reference measurements. Over and above the reasons why the present invention, in its embodiments, patentably distinguishes from the Reymond et al. patents, the present invention distinguishes from Fenimore, Mitchelson, Gourlay and Schulz as specifically avoiding comparison of actual measurements to reference measurements.